.. option:: offset=int
- Start I/O at the provided offset in the file, given as either a fixed size or
- a percentage. If a percentage is given, the next ``blockalign``-ed offset
- will be used. Data before the given offset will not be touched. This
+ Start I/O at the provided offset in the file, given as either a fixed size in
+ bytes or a percentage. If a percentage is given, the next ``blockalign``-ed
+ offset will be used. Data before the given offset will not be touched. This
effectively caps the file size at `real_size - offset`. Can be combined with
:option:`size` to constrain the start and end range of the I/O workload.
+ A percentage can be specified by the percentage number plus 1 with preceding '-'.
+ For example, -1 is parsed as 0%, -10 is parsed as 9%, -101 is parsed as 100%.
.. option:: offset_increment=int